Degenerate Higher-Order Scalar-Tensor (DHOST) theories

Abstract

This contribution reviews scalar-tensor theories whose Lagrangian contains second-order derivatives of a scalar field but nevertheless propagate only one scalar mode (in addition to the usual two tensor modes), and are thus not plagued with the Ostrodradsky instability. These theories, which encompass the so-called Horndeski and Beyond Horndeski theories, have recently been fully classified up to cubic order in second-order derivatives. After introducing these theories, I present a few phenomenological aspects. In cosmology, these theories can be included in the unified effective description of dark energy and modified gravity. Finally, neutron star solutions in some specific models are discussed.

9 pages, no figure; proceedings of Rencontres de Moriond 2017 (session gravitation)

References in corpus (8)

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• Perturbations and quasi-normal modes of black holes with time-dependent scalar hair in shift-symmetric scalar-tensor theories
• Disformal Transition of a Black Hole to a Wormhole in Scalar-Tensor Horndeski Theory
• Generating enhanced primordial GWs during inflation with intermittent violation of NEC and diminishment of GW propagating speed
• The shape of Scalar Gauss-Bonnet Gravity
• Large-scale structure in mimetic Horndeski gravity
• Scalar-tensor cosmologies without screening
• A local self-tuning mechanism for the cosmological constant
• UV sensitive one-loop matter power spectrum in degenerate higher-order scalar-tensor theories
• Disformal mappings of spherical DHOST geometries
• Thermodynamic and observational constraints on black holes with primary hair in Beyond Horndeski Gravity: Stability and shadows
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